Tyrosinase-mediated oxidation of acetaminophen to 4-acetamido-o-benzoquinone

Investigating Paracetamol's Role as a Potential Treatment for Parkinson's Disease: Ab Initio Analysis of Dopamine, l-DOPA, Paracetamol, and NAPQI Interactions with Enzymes Involved in Dopamine Metabolism

Recently, it was found that paracetamol can extend the therapeutic window of l-DOPA treatment for Parkinson's disease [Golding (2019) BJPharm, 4(2), Article 619]. It has been posited that the effect could be due to paracetamol and its metabolite, NAPQI, inhibiting pain signals in the spinal column. In this work, we examine the possibility that the therapeutic effect of the paracetamol for the Parkinson's disease patient may be due to an inhibition of the enzymes that metabolize dopamine and/or l-DOPA, thus effectively extending the lifetime of the l-DOPA treatment. In this work, we use the M062X/6-311+G* level of theory to calculate the electronic binding energies (including explicit desolvation) of several ligands (paracetamol, NAPQI, dopamine, and l-DOPA) with a series of enzymes important to the production and metabolism of dopamine and compare them to calculated binding energy values for the natural substrates for those enzymes in order to predict possible inhibition. Benchmark interaction energies for a subset of the systems studied are calculated using the more accurate second-order Møller-Plesset perturbation (MP2) method in order to calibrate the accuracy of the M062X method. If we assume that the interaction energies calculated here can serve as a proxy for in vivo inhibition, then we can predict that paracetamol and NAPQI should not inhibit the natural production of dopamine and may in fact inhibit the metabolism of l-DOPA and dopamine, thus extending the length of l-DOPA treatments.

Flow injection tyrosinase biosensor for direct determination of acetaminophen in human urine

An amperometric biosensor compatible with a flow injection analysis (FIA) for highly selective determination of acetaminophen (APAP) in a sample of human urine was developed. This biosensor is also suitable for use in the routine pharmaceutical practice. To prove this statement, two different commercially available pharmaceutical formulations were analyzed. This nano-(bio)electroanalytical device was made from a commercially available screen-printed carbon electrode covered by a thin layer of non-functionalized graphene (NFG) as amperometric transducer. A biorecognition layer was prepared from mushroom (Agaricus bisporus) tyrosinase (EC 1.14.18.1) cross-linked using glutaraldehyde, where resulting aggregates were covered by Nafion^®, a known ion exchange membrane. Owing to the use of tyrosinase and presence of NFG, the developed analytical instrument is able to measure even at potentials of 0 V. Linear ranges differ according to choice of detection potential, namely up to 130 μmol L^-1 at 0 V, up to 90 μmol L^-1 at -0.1 V, and up to 70 μmol L^-1 at -0.15 V. The first mentioned linear range is described by the equation I_p [μA] = 0.236 - 0.1984c [μmol L^-1] and correlation coefficient r = 0.9987; this equation was used to quantify the content of APAP in each sample. The limit of detection of APAP was estimated to be 1.1 μmol L^-1. A recovery of 96.8% (c = 25 μmol L^-1, n = 5 measurements) was calculated. The obtained results show that FIA is a very selective method for APAP determination, being comparable to the chosen reference method of reversed-phase high-performance liquid chromatography.

Bananas decrease acetaminophen potency in in vitro assays

Edible portions of bananas contain high levels of polyphenol oxidase, which catalyzes reactions in the melanin formation pathway. Tyrosine, a physiological substrate of polyphenol oxidase, has an analogous structure to acetaminophen. We investigated whether banana extract causes structural changes in acetaminophen and a decrease in its potency. Acetaminophen concentration in banana extract was measured under different conditions to characterize incompatibility. Reaction products in solution were identified using liquid chromatography/electrospray ionization/mass spectrometry (LC/ESI/MS). Acetaminophen potency decreased with time in the presence of banana extract. The reaction proceeded most efficiently in temperatures 30-37°C and neutral to weakly acidic conditions. Molecular ion peaks derived from the oxidized catechol moiety of acetaminophen were identified in LC/ESI/MS spectra. Our findings suggest that incorporation or simultaneous administration of acetaminophen medication and banana juice may result in decreased efficacy of the clinically important drug. This interaction is likely due to the oxidation of acetaminophen by polyphenol oxidase activity in banana pulp. Therefore, we investigated and characterized a novel interaction between bananas and acetaminophen. To establish a safe and effective antipyretic analgesic regimen using acetaminophen, future studies of this interaction are expected to be performed in humans.

Biosensor-based real-time monitoring of paracetamol photocatalytic degradation

This paper presents for the first time the integration of a biosensor for the on-line, real-time monitoring of a photocatalytic degradation process. Paracetamol was used as a model molecule due to its wide use and occurrence in environmental waters. The biosensor was developed based on tyrosinase immobilization in a polyvinylalcohol photocrosslinkable polymer. It was inserted in a computer-controlled flow system installed besides a photocatalytic reactor including titanium dioxide (TiO2) as photocatalyst. It was shown that the biosensor was able to accurately monitor the paracetamol degradation with time. Compared with conventional HPLC analysis, the described device provides a real-time information on the reaction advancement, allowing a better control of the photodegradation process.

Synthesis and characterization of combined cross-linked laccase and tyrosinase aggregates transforming acetaminophen as a model phenolic compound in wastewaters

Laccase (EC 1.10.3.2) and tyrosinases (EC 1.14.18.1) are ubiquitous enzymes present in nature as they are known to originate from bacteria, fungi, plants, etc. Both laccase and tyrosinase are copper-containing phenoloxidases requiring readily available O2 without auxiliary cofactor for their catalytic transformation of numerous phenolic substrates. In the present study, laccase and tyrosinase have been insolubilized as combined crosslinked enzyme aggregates (combi-CLEA) using chitosan, a renewable and biodegradable polymer, as crosslinker. The combi-CLEA, with specific activity of 12.3 U/g for laccase and 167.4 U/g for tyrosinase, exhibited high enzymatic activity at pH5-8 and temperature at 5-30°C, significant resistance to denaturation and no diffusional restriction to its active site based upon the Michaelis-Menten kinetic parameters. Subsequently, the combi-CLEA was applied to the transformation of acetaminophen as a model phenolic compound in samples of real wastewaters in order to evaluate the potential efficiency of the biocatalyst. In batch mode the combi-CLEA transformed more than 80% to nearly 100% of acetaminophen from the municipal wastewater and more than 90% from the hospital wastewater. UPLC-MS analysis of acetaminophen metabolites showed the formation of its oligomers as dimers, trimers and tetramers due to the laccase and 3-hydroxyacetaminophen due to the tyrosinase.

Mechanism of acetaminophen oxidation by the peroxidase-like activity of methemoglobin

Oxidation of acetaminophen by human methemoglobin in the presence of H(2)O(2) has been kinetically studied in the present paper. The drug showed a protective effect against the H(2)O(2)-induced irreversible inactivation of the protein, thus indicating the competition among both ligands, H(2)O(2) and acetaminophen for the protein. The stoichiometry of the reaction is variable and depends on relative initial concentrations of H(2)O(2) and the drug owing to their competitive behavior. In addition and unexpectedly, the protein exhibits non Michaelian kinetics against both acetaminophen and H(2)O(2) under steady-state conditions and shows negative co-operativity with Hill coefficients in the 0.3-0.7 range. Therefore, these data were compared to those obtained with myoglobin under similar experimental conditions, and the same results were observed. This led us to propose a mechanism for the peroxidase-like activity of hemoglobin, which accounts for the experimental results obtained herein. The steady-state rate equation for this mechanism has been obtained and is also consistent with the experimental data, thus indicating the goodness of the model proposed herein. The results presented in this work provide new insights into the oxidation mechanism of acetaminophen.

Biochemical mechanism of acetaminophen (APAP) induced toxicity in melanoma cell lines

In this work, we investigated the biochemical mechanism of acetaminophen (APAP) induced toxicity in SK-MEL-28 melanoma cells using tyrosinase enzyme as a molecular cancer therapeutic target. Our results showed that APAP was metabolized 87% by tyrosinase at 2 h incubation. AA and NADH, quinone reducing agents, were significantly depleted during APAP oxidation by tyrosinase. The IC(50) (48 h) of APAP towards SK-MEL-28, MeWo, SK-MEL-5, B16-F0, and B16-F10 melanoma cells was 100 microM whereas it showed no significant toxicity towards BJ, Saos-2, SW-620, and PC-3 nonmelanoma cells, demonstrating selective toxicity towards melanoma cells. Dicoumarol, a diaphorase inhibitor, and 1-bromoheptane, a GSH depleting agent, enhanced APAP toxicity towards SK-MEL-28 cells. AA and GSH were effective in preventing APAP induced melanoma cell toxicity. Trifluoperazine and cyclosporin A, inhibitors of permeability transition pore in mitochondria, significantly prevented APAP melanoma cell toxicity. APAP caused time and dose-dependent decline in intracellular GSH content in SK-MEL-28, which preceded cell toxicity. APAP led to ROS formation in SK-MEL-28 cells which was exacerbated by dicoumarol and 1-bromoheptane whereas cyslosporin A and trifluoperazine prevented it. Our investigation suggests that APAP is a tyrosinase substrate, and that intracellular GSH depletion, ROS formation and induced mitochondrial toxicity contributed towards APAP's selective toxicity in SK-MEL-28 cells.

Characterization of the monophenolase activity of tyrosinase on betaxanthins: the tyramine-betaxanthin/dopamine-betaxanthin pair

Tyrosinase or polyphenol oxidase (EC 1.14.18.1) is the key enzyme responsible for melanin biosynthesis and for the enzymatic browning of fruits and vegetables. Although the function of tyrosinase in the secondary metabolism of plants remains unclear, it has been proposed that the enzyme plays a role in the betalain biosynthetic pathway. Betalains are an important class of water-soluble pigments, characteristic of plants belonging to the order Caryophyllales. In the present work, the betaxanthins tyramine-betaxanthin (miraxanthin III) and dopamine-betaxanthin (miraxanthin V) are reported as new natural substrates for tyrosinase. The result of the diphenolase activity of the enzyme on dopamine-betaxanthin was a series of products identified by HPLC and ESI-MS as quinone-derivatives. Data indicate that dopamine-betaxanthin-quinone is obtained and evolves to more stable species by intramolecular cyclization. The kinetic parameters evaluated for the diphenolase activity were V(m) = 74.4 microM min(-1), K(m) = 94.7 microM. Monophenolase activity on tyramine-betaxanthin yielded the same compounds in the absence of a reducing agent, but when ascorbic acid was present enzymatic conversion to dopamine-betaxanthin could be found. For the first time, kinetic characterization of the monophenolase activity of tyrosinase on betaxanthins is provided (V(m) = 10.4 microM min(-1) and K(m) = 126.9 microM) and a lag period is described and analyzed according to the mechanism of action of the enzyme. The high affinity shown by tyrosinase for these substrates may be indicative of a previously unconsidered physiological role in betalain metabolism. A possible mechanism for the formation of 2-descarboxy-betacyanins from tyramine-betaxanthin by tyrosinase is also discussed.

Melanization immune responses in mosquito vectors

The production and deposition of melanin pigments on invading pathogens and parasites represents a unique, innate immune response in the phylum Arthropoda. This immune response has started to receive considerable attention because of the potential to exploit this mechanism to control mosquito-borne diseases. In this article, we summarize knowledge about this complex biochemistry, the use of melanin biosynthesis in diverse physiological processes and the gaps in knowledge that must be addressed if this immune process is to be manipulated in genetic-based control strategies.

Catalytic oxidation of acetaminophen by tyrosinase in the presence of L-proline: a kinetic study

A kinetic study of acetaminophen oxidation by tyrosinase in the presence of a physiological nucleophilic agent such as the amino acid L-proline is performed in the present paper. The o-quinone product of the catalytic activity, 4-acetamido-o-benzoquinone, becomes unstable through the chemical addition of L-proline, in competition with the nucleophilic addition of hydroxide ion from water. In both cases, the catechol intermediate, 3(')-hydroxyacetaminophen, is generated, as can be demonstrated by liquid chromatography. When the effect of the presence of the nucleophilic agent on the time course of the enzymatic reaction was kinetically analyzed, it was seen to decrease the duration of the lag period and increase the steady-state rate. Rate constants for the reaction of 4-acetamido-o-benzoquinone with water and L-proline were also determined. The results obtained in this paper open a new possibility to acetaminophen toxicity, that has been attributed hitherto to its corresponding p-quinone, N-acetyl-p-benzoquinone imine.